The goal of this study is to gain a better understanding of how the lung utilizes immune mechanisms in its defense against airborne antigenic agents. We will begin by studying functional lymphocyte subpopulations (T and B) in the air spaces of normal human lungs. Lung lymphocytes obtained by segmental bronchial lavage will be characterized by using membrane markers and response to specific mitogens. The study will focus on: (a) the frequency of T and B lymphocytes in the normal lung; (b) relative contributions that these cells make toward local cellular and humoral immune responses in the lung; (c) a better understanding of the function and life history of T lymphocytes in the lung using an animal model.